physics as necessary but not sufficient to explain causation in complex systems

Ellis (2008) has an account of the nature of top-down causation in complex systems. He says there are at least five established forms of top-down causation – ways in which the higher level properties of a system can have causal power over the lower level elements (in contrast to the reductive view which would say that all behaviour of a system can be explained by the lower level properties : the physics is primary approach).

For me, the value of the paper is a single thought: physics provides the necessary, but not sufficient conditions, for explaining human behaviour. Without our physical natures – our undeniable existence as material beings, governed by four primary physical forces – we would not be, but to understand our being you need more than an account of the component materials and their governing forces.

Probably an obvious point, but succinctly put and useful to have on hand when faced with reductionists, or when trying to figure out the proper role of human agency in a strictly physical universe.